A sheet is a rope or line for controlling the set of a sail on a sailing vessel. Conventionally the sheet is passed through one or more pulley blocks or sheaves attached to the sail (or boom) and the hull of the vessel. In light weather it is desirable that the sheet runs freely through the pulley block. However, when hauling in the sail in heavy weather it is desirable that the pulley block may incorporate a ratchet to prevent or inhibit the sheet running out through the pulley block e.g. when the helmsman (or crew) adjusts his hands on the sheet.
It is known to provide a pulley block with a ratchet which can be manually selectively rendered operative and inoperative.
It is also known to provide a pulley block with a ratchet which is inoperative when light loads are applied to the block. This known pulley block comprises a ratchet wheel with outwardly directed teeth and a pawl for engaging the teeth. When intermediate loads are applied to the block the pawl may engage only partially with the teeth. Consequently ratchet action may not be positive, the ratchet repeatedly becoming operative and then inoperative, and the teeth and the pawl are subject to heavy wear.
The present invention aims to provide an improved pulley block or sheave incorporating a ratchet mechanism.